Lead-in seal and lamp utilizing same

ABSTRACT

A lead-in seal of the type having a metal foil seal member sealed into an envelope, comprising a relatively narrow intermediate foil tab member connected between the foil seal member and a conductor. The result is reduced stress in the seal and less likelihood of cracking.

BACKGROUND OF THE INVENTION

The invention is in the field of lamps and other devices having currentlead-in conductors sealed in and through a bulb or envelope by means ofcurrent-conductive foil members.

U.S. Pat. No. 3,685,880 to John C. Sobieski, for example, discloses alamp containing a pair of electrodes each connected to a separatelead-in conductor by a thin metal foil member, the foil members beinghermetically sealed in the lamp envelope at seal regions, the endregions of the electrodes and lead-in conductors being embedded in theseal regions. The electrodes and lead-in conductors are attached to therespective foil members by positioning their end regions to overlapregions of the foil member, and spot welding these overlapped regionstogether. Typically, the lead-in conductors and the foil members aremade of molybdenum, and, in an arc lamp, the electrodes are tungstenrods. To improve the spot-welded connections, both electrically andmechanically, small platinum-coated molybdenum foil pads have beenplaced at the spot-weld locations, between the molybdenum seal foilmember and the tungsten electrodes and/or the molybdenum lead-inconductors, prior to spot welding. The improvement thus achieved isrelatively greater for the welds of the foil member to the tungstenelectrode rods. However, it has been found that this improvement in weldbonding is accompanied by an increased tendency for cracking of theenvelope material at the seal region.

SUMMARY OF THE INVENTION

Objects of the invention are to provide an improved foil-type seal forlamps and the like, and to provide such a seal which has good electricaland mechanical properties, and good reliability of remaining intactwithout cracking.

The invention comprises, briefly and in a preferred embodiment, alead-in seal having a thin conductive foil member sealed into anenvelope, such as into a stem integral with a lamp bulb or housing, athin conductive tab member attached to the foil member and extendingtherefrom, and an electrode attached to the extending portion of the tabmember and extending into the interior of the lamp bulb, the attachedend of the electrode being spaced from the adjacent edge of the foil.Preferably, the width of the tab member is about the same as thediameter of the electrode to which it is attached, and may be thickerthan the foil, if required for conducting the lamp operating currentwithout overheating. The tab preferably is shaped in the form of adouble bend such that its end regions lie in parallel planes. In thepreferred embodiment, the electrode is a tungsten rod, the tab member isa platinum-coated molybdenum foil, and the seal member is molybdenumfoil, and a molybdenum lead-in conductor is attached to the seal foil atthe end thereof opposite from the tab, the electrode and lead-inconductor being substantially axially aligned.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a top view of a compact high intensity arc lamp provided witha foil lead-in seal in accordance with a preferred embodiment of theinvention.

FIG. 2 is an enlarged side view of a lead-in seal region of the lamp ofFIG. 1.

FIGS. 3 and 4 are side and top views, respectively, of a prior art typeof foil seal arrangement.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The compact high intensity arc lamp 11 in FIG. 1 comprises an envelopeof quartz or other suitable vitreous material having a bulb portion 12and stem portions 13 and 14 extending therefrom on opposite sidesthereof, on a common axis. Elongated tungsten rod anode and cathodeelectrodes 16 and 17 are positioned on the axis of the lamp with theinner ends thereof spaced apart within the bulb portion 12, andrespectively extend into the anode stem 13 and cathode stem 14. Thetungsten anode rod 16 is part of the anode lead-in assembly, whichfurther comprises a molybdenum lead-in wire 18 having an end 19 spacedfrom the outer end of the anode 16, the lead-in 18 and anode rod 16being substantially axially aligned. The inner end region 19 of thelead-in wire 18 overlaps and is spot-welded to an end portion of amolybdenum thin foil member 21. The end region 19 of the lead-in wiremay be swaged or otherwise flattened to facilitate a good weld. A thinfoil tab member 22 has an end region 23 positioned to overlap a portionof the other end of the foil 21, and is spot-welded thereto. Theremaining end region 24 of the tab 22 is positioned to overlap an endregion of the anode rod 16, and is spot-welded thereto. Preferably, thetab 22 is provided with a double bend, as shown in FIG. 2, so that theend region 23 and 24 thereof lie in spaced apart parallel planes, sothat the anode 16 and lead-in wire 18 will be substantially in axialalignment. The intermediate portion 26 of the tab 22 between its endregions 23 and 24 may be inclined at an angle of approximately 45° asshown in FIG. 2.

The outer end of the cathode rod 17 is shown spot-welded directly to amolybdenum seal foil 31, and a cathode lead-in wire 32, preferably ofmolybdenum, is spot-welded to the remaining end region of the foil 31,the welded end region 33 of the lead-in wire 32 having been flattened orswaged to facilitate the welding.

After the anode and cathode lead-in electrode assemblies have beenprepared, they are properly positioned with their inner ends within thebulb portion 12, and the bulb is evacuated and filled with suitable gas,and a metal halide such as indium triiodide, if desired, and the endregions of the stems 13 and 14 are heated and flattened by pairs ofjaws, for example as disclosed in the above-referenced Sobieski patent,to form anode and cathode seal regions 36 and 37, respectively, in whichseal regions the quartz material of the bulb wets the foils 21 and 31,thus providing hermetic sealing.

The foil tab 22 of the invention is preferably molybdenum coated withplatinum, similar to the spot-welding pads that have been usedpreviously. The tab 22 preferably has a width approximately equal to thediameter of the tungsten rod 16 to which it is welded, and the tab 22may be thicker than the seal foil 21, in order to adequately carry theoperating current of the lamp without overheating. In a practicalembodiment, the platinum-plated molybdenum tab 22 is 3/1000 of an inchthick, and the molybdenum sealing foil 21 is 9/10,000 of an inch thick.

The invention, comprising the elongated connector tab 22 between thesealing foil 21 and the electrode 16, achieves its objective ofconsiderably reducing the number of seals 36 which crack duringoperation of the lamp, the anode seal 36 having been particularly proneto cracking. This achievement is believed due not only to the elongatedfeature of the tab 22, but also due to its double bend which providesthe oblique intermediate section 26. Both of these features appear toreduce stress in the seal 36 after the lamp is completed. The reason forthis improvement is believed due to a tendency for a stress to developand remain in the seal region 36 when the former technique was employedof positioning a foil platinum-coated pad between the sealing foil 21and electrode 16. Tabs similar to the tab 22 can be interposed betweenthe foil 21 and lead-in wire 18, and between the foil 31 and electrode17 and lead-in wire 32, respectively.

FIGS. 3 and 4 illustrate this prior construction, in which aplatinum-coated molybdenum foil pad 41 was interposed between the weldregions of the anode 16 and the sealing foil 21 prior to the step ofspot welding these members together. It is believed that during the spotwelding, the foil pad 41 curled slightly upwardly at its edges, towardthe round rod 16, causing narrow spaces between these curled edges andthe sealing foil 21, and also narrow spaces between these curled edgesand the electrode rod 16, and during the sealing operation the quartzmaterial of the envelope was unable to adequately penetrate into andfill these narrow spaces, which resulted in setting up a stress in theseal. It should be noted that, due to its extreme hardness, it isrelatively difficult to swage or flatten the spot-welded end of thetungsten rod 16, as can more readily be done at the spot-welded end 19of the molybdenum lead-in wire 18, to provide a broader area of spotwelding.

Another achievement of the invention is the prevention of corrosion ofthe molybdenum seal foil 21 by metal halide or other corrosive vaporcontained in the bulb 12 and which can seep along the electrode 16within the stem 13, to the outer welded end of the electrode. Theplatinum coating on the tab 22 resists corrosion, and thecorrosion-prone molybdenum foil 21 is completely sealed and encased bythe quartz housing material so the corrosive vapors cannot reach it. Theuse of a single platinum-coated foil interconnecting the members 16 and18 is undesirable because platinum is not wetted by quartz as well as isbare molybdenum foil.

While preferred embodiments of the invention have been shown anddescribed, various other embodiments and modifications thereof willbecome apparent to persons skilled in the art and will fall within thescope of the invention as defined in the following claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:
 1. A seal comprising an envelope of vitreous material, aconductive foil seal member, an elongated electrical conductorpositioned to have an end thereof axially spaced from an edge of saidfoil seal member, and a conductive foil tab member extendingsubstantially axially between and interconnecting said foil seal memberand said elongated conductor, said foil seal member being hermeticallysealed in said material of the envelope.Iadd., said tab member beingprovided with a double bend to provide an angled intermediate regionjoining first and second end regions thereof which lie in parallelplanes, said first end region overlapping and being attached to a regionof said foil member and said second and region overlapping and beingattached to the end region of said elongated conductor.Iaddend..
 2. Aseal as claimed in claim 1, in which said tab member is elongated withone end region thereof overlapping and welded to a region of said foilseal member and the other end region thereof overlapping and welded tothe end region of said conductor.
 3. A seal as claimed in claim 1, inwhich said envelope material is quartz, said foil seal member ismolybdenum, said elongated conductor is tungsten, and said tab member isplatinum-coated molybdenum.
 4. A seal as claimed in claim 1, in whichthe width of said tab member is narrower than the width of said sealmember and is substantially equal to the width or diameter of saidelongated conductor.
 5. A seal as claimed in claim 4, in which said foiltab member is thicker than said foil seal member. .[.6. A seal asclaimed in claim 1, in which said tab member is provided with a doublebend to provide an angled intermediate region joining first and secondend regions thereof which lie in parallel planes, said first end regionoverlapping and being attached to a region of said foil seal member andsaid second end region overlapping and being attached to the end regionof said elongated conductor..].
 7. A lamp comprising an envelope ofvitreous material, a conductive foil seal member, and first and secondelongated electrical conductors, said foil seal member and conductorsbeing aligned substantially axially with the foil seal member betweenthe conductors, and means connecting the conductors to the foil sealmember at opposed ends thereof, at least one of said means comprising anaxial spacing between the foil seal member and one of said conductors, aconductive foil tab member extending substantially axially between thefoil seal member and the last-mentioned conductor and connected theretoat respective opposed ends of the tab member, said foil seal memberbeing hermetically sealed in said material of the envelope, said firstelongated conductor extending within said envelope and said secondelongated conductor extending out of said envelope.Iadd., said foil tabmember being provided with a double bend to provide an angledintermediate region joining first and second end regions thereof whichlie in parallel planes, said first end region overlapping and beingattached to a region of said foil member and said second and regionoverlapping and being attached to the end region of said elongatedconductor.Iaddend..
 8. A lamp as claimed in claim 7, in which said tabmember is elongated with one end region thereof overlapping and weldedto a region of said foil seal member and the other end region thereofoverlapping and welded to the end region of the conductor.
 9. A lamp asclaimed in claim 7, in which said envelope material is quartz, said foilseal member is molydenum, said first conductor is tungsten, said tabmember is platinum-coated molybdenum, and said second conductor ismolybdenum.
 10. A lamp as claimed in claim 7, in which the width of saidtab member is narrower than the width of said seal member and issubstantially equal to the width or diameter of said elongatedconductor.
 11. A lamp as claimed in claim 10, in which said foil tabmember is thicker than said foil seal member. .[.12. A lamp as claimedin claim 7, in which said foil tab member is provided with a double bendto provide an angled intermediate region joining first and second endregions thereof which lie in parallel planes, said first end regionoverlapping and being attached to a region of said foil seal member andsaid second end region overlapping and being attached to the end regionof the conductor..].
 13. A lamp as claimed in claim 7, in which saidenvelope comprises a bulb and a stem extending from said bulb, saidhermetic sealing of the foil seal member being at the end region of saidstem away from said bulb, said first elongated conductor extendingthrough said stem and into said bulb, said second elongated conductorextending from said end of the stem, and said means connecting saidfirst conductor to said foil seal member comprising said foil tab memberextending between and connected to the foil seal member and firstconductor. .Iadd.14. A lamp comprising an envelope of vitreous material,a conductive foil seal member, and first and second elongated electricalconductors, said foil seal member and conductors being alignedsubstantially axially with the foil seal member between the conductors,and means connecting the conductors to the foil seal member at opposedends thereof, at least one of said means comprising an axial spacingbetween the foil seal member and one of said conductors, a conductivefoil tab member extending substantially axially between the foil sealmember and the last-mentioned conductor and connected thereto atrespective opposed ends of the tab member, said foil seal member beinghermetically sealed in said material of the envelope, said firstelongated conductor extending within said envelope and said secondelongated conductor extending out of said envelope, and in which saidenvelope material is quartz, said foil seal member is molybdenum, saidfirst conductor is tungsten, said tab member is platinum-coatedmolybdenum, and said second conductor is molybdenum..Iaddend.